/* 
 *  Copyright (c) 2011—2013 Panguso.com. All rights reserved. 
 *  File Name:  Base64.java                                      
 *  File Contents Outline :
 *  File  Create Date:   2012年7月30日
 *  File Version#: Revision#: #1                  
 *  File  Latest Modify Date : 2013年1月16日
 *  File Author :  bachuan@panguso.com
 */

package storage.util;


public class Base64 {

    private static final byte[] encodingTable = {
        (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E',
        (byte) 'F', (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J',
        (byte) 'K', (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O',
        (byte) 'P', (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T',
        (byte) 'U', (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y',
        (byte) 'Z', (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd',
        (byte) 'e', (byte) 'f', (byte) 'g', (byte) 'h', (byte) 'i',
        (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n',
        (byte) 'o', (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's',
        (byte) 't', (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x',
        (byte) 'y', (byte) 'z', (byte) '0', (byte) '1', (byte) '2',
        (byte) '3', (byte) '4', (byte) '5', (byte) '6', (byte) '7',
        (byte) '8', (byte) '9', (byte) '+', (byte) '/'
    };
    private static final byte[] decodingTable;

    static {

        decodingTable = new byte[128];

        for (int i = 0; i < 128; i++) {

            decodingTable[i] = (byte) -1;

        }

        for (int i = 'A'; i <= 'Z'; i++) {

            decodingTable[i] = (byte) (i - 'A');

        }

        for (int i = 'a'; i <= 'z'; i++) {

            decodingTable[i] = (byte) (i - 'a' + 26);

        }

        for (int i = '0'; i <= '9'; i++) {

            decodingTable[i] = (byte) (i - '0' + 52);

        }

        decodingTable['+'] = 62;

        decodingTable['/'] = 63;

    }

    public static byte[] encode(byte[] data, int offset) {

        byte[] bytes;

        int realCount = data.length - offset;

        int modulus = realCount % 3;

        if (modulus == 0) {

            bytes = new byte[(4 * realCount) / 3];

        } else {

            bytes = new byte[4 * ((realCount / 3) + 1)];

        }

        int dataLength = (data.length - modulus);

        int a1;

        int a2;

        int a3;

        for (int i = offset, j = 0; i < dataLength; i += 3, j += 4) {

            a1 = data[i] & 0xff;

            a2 = data[i + 1] & 0xff;

            a3 = data[i + 2] & 0xff;

            bytes[j] = encodingTable[(a1 >>> 2) & 0x3f];

            bytes[j + 1] = encodingTable[((a1 << 4) | (a2 >>> 4)) & 0x3f];

            bytes[j + 2] = encodingTable[((a2 << 2) | (a3 >>> 6)) & 0x3f];

            bytes[j + 3] = encodingTable[a3 & 0x3f];

        }

        int b1;

        int b2;

        int b3;

        int d1;

        int d2;

        switch (modulus) {

            case 0: /*
                 * nothing left to do
                 */

                break;

            case 1:

                d1 = data[data.length - 1] & 0xff;

                b1 = (d1 >>> 2) & 0x3f;

                b2 = (d1 << 4) & 0x3f;

                bytes[bytes.length - 4] = encodingTable[b1];

                bytes[bytes.length - 3] = encodingTable[b2];

                bytes[bytes.length - 2] = (byte) '=';

                bytes[bytes.length - 1] = (byte) '=';

                break;

            case 2:

                d1 = data[data.length - 2] & 0xff;

                d2 = data[data.length - 1] & 0xff;

                b1 = (d1 >>> 2) & 0x3f;

                b2 = ((d1 << 4) | (d2 >>> 4)) & 0x3f;

                b3 = (d2 << 2) & 0x3f;

                bytes[bytes.length - 4] = encodingTable[b1];

                bytes[bytes.length - 3] = encodingTable[b2];

                bytes[bytes.length - 2] = encodingTable[b3];

                bytes[bytes.length - 1] = (byte) '=';

                break;

        }

        return bytes;

    }

    public static byte[] decode(byte[] data) {

        byte[] bytes;

        byte b1;

        byte b2;

        byte b3;

        byte b4;

        data = discardNonBase64Bytes(data);

        if (data[data.length - 2] == '=') {

            bytes = new byte[(((data.length / 4) - 1) * 3) + 1];

        } else if (data[data.length - 1] == '=') {

            bytes = new byte[(((data.length / 4) - 1) * 3) + 2];

        } else {

            bytes = new byte[((data.length / 4) * 3)];

        }

        for (int i = 0, j = 0; i < (data.length - 4); i += 4, j += 3) {

            b1 = decodingTable[data[i]];

            b2 = decodingTable[data[i + 1]];

            b3 = decodingTable[data[i + 2]];

            b4 = decodingTable[data[i + 3]];

            bytes[j] = (byte) ((b1 << 2) | (b2 >> 4));

            bytes[j + 1] = (byte) ((b2 << 4) | (b3 >> 2));

            bytes[j + 2] = (byte) ((b3 << 6) | b4);

        }

        if (data[data.length - 2] == '=') {

            b1 = decodingTable[data[data.length - 4]];

            b2 = decodingTable[data[data.length - 3]];

            bytes[bytes.length - 1] = (byte) ((b1 << 2) | (b2 >> 4));

        } else if (data[data.length - 1] == '=') {

            b1 = decodingTable[data[data.length - 4]];

            b2 = decodingTable[data[data.length - 3]];

            b3 = decodingTable[data[data.length - 2]];

            bytes[bytes.length - 2] = (byte) ((b1 << 2) | (b2 >> 4));

            bytes[bytes.length - 1] = (byte) ((b2 << 4) | (b3 >> 2));

        } else {

            b1 = decodingTable[data[data.length - 4]];

            b2 = decodingTable[data[data.length - 3]];

            b3 = decodingTable[data[data.length - 2]];

            b4 = decodingTable[data[data.length - 1]];

            bytes[bytes.length - 3] = (byte) ((b1 << 2) | (b2 >> 4));

            bytes[bytes.length - 2] = (byte) ((b2 << 4) | (b3 >> 2));

            bytes[bytes.length - 1] = (byte) ((b3 << 6) | b4);

        }

        return bytes;

    }

    public static byte[] decode(String data) {

        byte[] bytes;

        byte b1;

        byte b2;

        byte b3;

        byte b4;

        data = discardNonBase64Chars(data);

        if (data.charAt(data.length() - 2) == '=') {

            bytes = new byte[(((data.length() / 4) - 1) * 3) + 1];

        } else if (data.charAt(data.length() - 1) == '=') {

            bytes = new byte[(((data.length() / 4) - 1) * 3) + 2];

        } else {

            bytes = new byte[((data.length() / 4) * 3)];

        }

        for (int i = 0, j = 0; i < (data.length() - 4); i += 4, j += 3) {

            b1 = decodingTable[data.charAt(i)];

            b2 = decodingTable[data.charAt(i + 1)];

            b3 = decodingTable[data.charAt(i + 2)];

            b4 = decodingTable[data.charAt(i + 3)];

            bytes[j] = (byte) ((b1 << 2) | (b2 >> 4));

            bytes[j + 1] = (byte) ((b2 << 4) | (b3 >> 2));

            bytes[j + 2] = (byte) ((b3 << 6) | b4);

        }

        if (data.charAt(data.length() - 2) == '=') {

            b1 = decodingTable[data.charAt(data.length() - 4)];

            b2 = decodingTable[data.charAt(data.length() - 3)];

            bytes[bytes.length - 1] = (byte) ((b1 << 2) | (b2 >> 4));

        } else if (data.charAt(data.length() - 1) == '=') {

            b1 = decodingTable[data.charAt(data.length() - 4)];

            b2 = decodingTable[data.charAt(data.length() - 3)];

            b3 = decodingTable[data.charAt(data.length() - 2)];

            bytes[bytes.length - 2] = (byte) ((b1 << 2) | (b2 >> 4));

            bytes[bytes.length - 1] = (byte) ((b2 << 4) | (b3 >> 2));

        } else {

            b1 = decodingTable[data.charAt(data.length() - 4)];

            b2 = decodingTable[data.charAt(data.length() - 3)];

            b3 = decodingTable[data.charAt(data.length() - 2)];

            b4 = decodingTable[data.charAt(data.length() - 1)];

            bytes[bytes.length - 3] = (byte) ((b1 << 2) | (b2 >> 4));

            bytes[bytes.length - 2] = (byte) ((b2 << 4) | (b3 >> 2));

            bytes[bytes.length - 1] = (byte) ((b3 << 6) | b4);

        }

//        for (int i = 0; i < bytes.length; i++) {
//            System.out.println("," + bytes[i]);
//        }

        return bytes;

    }

    private static byte[] discardNonBase64Bytes(byte[] data) {

        byte[] temp = new byte[data.length];

        int bytesCopied = 0;

        for (int i = 0; i < data.length; i++) {

            if (isValidBase64Byte(data[i])) {

                temp[bytesCopied++] = data[i];

            }

        }

        byte[] newData = new byte[bytesCopied];

        System.arraycopy(temp, 0, newData, 0, bytesCopied);

        return newData;

    }

    private static String discardNonBase64Chars(String data) {

        StringBuilder sb = new StringBuilder();

        int length = data.length();

        for (int i = 0; i < length; i++) {

            if (isValidBase64Byte((byte) (data.charAt(i)))) {

                sb.append(data.charAt(i));

            }

        }

        return sb.toString();

    }

    private static boolean isValidBase64Byte(byte b) {

        if (b == '=') {

            return true;

        } else if ((b < 0) || (b >= 128)) {

            return false;

        } else if (decodingTable[b] == -1) {

            return false;

        }

        return true;

    }

    public static String encode(String data, String charset) throws Exception {

        // byte[] result =  (data.getBytes("Unicode")); 

        if (data == null || data.length() == 0) {
            return data;
        }

        int offset = 0;

        // getBytes("unicode")转完后会在前头加上两字节”FE“ 

        byte[] result = encode(data.getBytes(charset), offset);

        StringBuilder sb = new StringBuilder(result.length);

        for (int i = 0; i < result.length; i++) {
            sb.append((char) result[i]);
        }

        return sb.toString();

    }

    public static String decode(String data, String charset) throws Exception {

        if (data == null || data.length() == 0) {
            return data;
        }

        return new String(Base64.decode(data), charset);

    }

    public static void main(String[] args) throws Exception {

        String data = "我们";

        String data1 = encode(data, "Unicode");

        String data2 = decode("//56AHgAYwA=", "Unicode");

        //System.out.println(data);

        //System.out.println(data1);

       // System.out.println(data2);

    }
}
